Aha. According to
this, the Performance Acceleration Mode setting is
Quote:
a technology for 875 mobos that increases overall performance by 3-5%. the 865 implements a technology known as gat, or gaming accelaration tech. It's for DDR400 (PC3200) or greater, in conjunction with a 800 mhz FSB CPU. It allows the RAM and CPU to run synchronously at 1:1 with the RAM on a 2x multiplier and CPU on 4x multiplier.
Other searches tell me that I should be able to turn this feature to "On". But it doesn't work with that new stick in the mix. For now, I'm just going to not worry about the tiny performance gain, and just leave it off.